HOWTO: Linux on the Intel iMac - Triple booting

Introduction - Why Macs?

I work as a System Administrator for a Computer Science Department and as a result I manage both server machines and lab machines. Some time ago the department decided (and I was in agreement) that it would be a good idea to offer the students additional variety in the computer lab by replacing some of the "Pee Cee" machines in the main undergrad lab with some Apple Macintosh systems. This would give students access to Mac OS X (pronounced "ten") in the lab in addition to Linux and Microsoft Windows.

Although Apple switched to Intel-based machines a few years ago, you can't just run their OS on any Intel/AMD machine as they have both licensing reasons and technical reasons why their OS should ONLY run on Apple hardware. They don't seem to be friendly to running Mac OS X inside of Virtualization either. Mr. Jobs, why do you hate us? I digress.

The first three years we had Macs in the lab they only ran Mac OS X and as time passed, fewer and fewer people used them. The usage slowdown was caused by a number of reasons that I'll not go into here. This year though, I decided not to give up on the Macs and to make them triple-boot... so if people don't want to use Mac OS X they don't have to, and the machines can get better utilization.

Looking for black magic?

Apple realized some time ago that people might want to dual-boot their new machines so they created Boot Camp. Indeed, Boot Camp does make it easy to dual-boot and they even give you all of the drivers needed to make Windows support their hardware... but what about triple-booting? Maybe someday the Boot Camp developers will implement triple-booting but for now it only supports dual-boot.

While Intel Macs are very similar to traditional PC machines there are a number of differences that make it challenging to setup a triple-boot scenario. The first thing is that they use an EFI type BIOS. The second thing is that they use a GPT (GUID Partition Table) type partitioning scheme rather than MBR. While GPT isn't as common yet, GPT is the wave of the future mainly because hard drive sizes are constantly growing.

I searched and searched for a recipe for triple-booting but most of the info I found was either outdated or for PowerPC based Macs. I finally found a HOWTO written by a fellow CS sysadmin that was both fairly recent and complete... although after doing it over and over I found a few points to refine and decided to write this.

Hardware I used

I did this recipe on two models of Intel iMacs:

1. The 2006 Core Duo unit
2. The 2009 Core 2 Duo unit

Although I only installed on two models of iMac, these intructions should work on any Intel-based Macintosh.

Reviewing the steps

1. Repartitioning the hard drive to make room for additional OSes. This is complicated because of the GPT and the final solution has a hybrid GPT/MBR partitioning scheme.
2. Installing a bootloader that understands the strange partitioning scheme needed that can actually assist.
3. Installing the OSes and making them work well with the hardware.

Repartitioning the a hard drive

This is an easy step because Apple includes the tool you need. It is a command line tool named diskutil. To see how your hard drive is currently partitioned run the following command from the terminal.

diskutil list disk0

You should see three partitions: 0 = GUID_partition_scheme, 1 = EFI, and 2 = Apple_HFS Macintosh HD. Of course sizes will vary depending on what size hard drive you have. To repartition the hard drive you use the following form:

diskutil resizeVolume disk0s2 {#}G \
"MS-DOS FAT32" Linux {#}G \
"MS-DOS FAT32" Windows {#}G \
"MS-DOS FAT32" Swap {#}G

You'd replace {#} with the desired number of GBs you want the drive to be. In my case the iMacs I'm using have 320GB hard drives but some space is lost because of overhead. I settled on the following:

diskutil resizeVolume disk0s2 200G \
"MS-DOS FAT32" Linux 43G \
"MS-DOS FAT32" Windows 50G \
"MS-DOS FAT32" Swap 4G

Note that the last partition you make won't actually be what you told it to be as it will use whatever is left.

Why specifiy "MS-DOS FAT32" as the partition type? Well diskutil is nice but it only knows about a handful of filesystems and Linux and Linux swap aren't included. When we install Linux we'll edit the existing partitions and change them to ext3 and Linux swap. For the Windows install we'll also change the partition set asside for Windows to NTFS.

There is some debate on whether it is safe to issue the diskutil repartitioning command from a live system or not. Some recommend booting from the Mac OS X install media so that the disk/partitions you are working with aren't live. I haven't had any trouble doing it from a live system with the drive in use. Perhaps it is a matter of changes from Tiger to Leopard. I've only used Leopard based machines and haven't had any trouble as diskutil has been totally non-destructive with the commands I've used.

Your mileage may vary so if you have data you care about on your Mac, make sure to back it up completely before starting.

After issuing the diskutil command in the form mentioned above, it will verify the disk first and then repartition it. It usually only takes a few minutes.

Installing a bootloader

Download rEFIt and install it. rEFIt is a fantastic bootloader and I wish the bootloaders we have for Linux were as fancy. rEFIt is not only a bootloader but it is smart and looks at the partitions and automatically makes entries when it finds an OS. It also assists in partitioning because it helps construct and maintain the needed GPT/MBR hybrid partition table. After installing rEFIt make sure to run the /efi/refit/enable-always.sh script so that the rEFIt bootloader will always appear rather than requiring holding down a key on the keyboard during power up.

Now that the bootloader is installed properly, reboot.

Syncing the partition table

One of the rEFIt features and an option on the rEFIt menu is "Start the Partition Tool". Any time you change the partition table select "Start the Partition Tool" from the rEFIt menu. It will let you create and manage the needed hybrid GPT/MBR partition table. Since we recently repartitioned the hard drive with the diskutil command you want to "Start the Partition Tool". Once back at the rEFIt menu, select "Reboot". I don't know if rebooting is technically required after running "Start the Partition Tool" but it seems to avoid some minor issues so I recommend it.

Installing Linux

I'm a big Fedora user and I recommend it. The Fedora 11 LiveCD media require three Linux partitions -- an ext3 /boot partition, an ext4 / partition, and a swap partition. You will notice from the diskutil command line I used above that I only made two partitions for Linux (one for / and one for swap). As a result you CAN NOT use the Fedora LiveCD media. In my early testing I tried making three partitions for Linux but either I made a mistake or it simply won't work. As a result I settled for having two partitions. So, to install Fedora 11 you'll need to use the DVD install media although the minimalistic netinstall media might work, I haven't tried it.

Put the install media into the optical drive and reboot. You can either hold down the c key on the keyboard to tell it to boot from the optical drive, or you can select the icon for the install media that shows up on the rEFIt menu. Please note that rEFIt reads all of the drives/partitions before showing the menu and will not refresh if you put in a CD/DVD... so if you put the install media in at the rEFIt menu, you'll have to reboot for it to see the media. I wish that rEFIt had an option to rescan for optical media insertion as well as a feature to eject inserted media... but it doesn't.

I'm not going to cover all of the install steps but just know you want to pick custom disk setup, select the first MS-DOS partition, edit it to make it ext3 and mounted on / and make sure to select the format option. Edit the last partition and make it Linux swap and format it. Also when it comes to the grub install screen make sure that it installs the grub bootloader to /dev/sda3 rather than the MBR of the drive. The install should proceed normally. When done reboot.

Since we changed the partitions some during the Linux install, at the rEFIt menu select "Start the Partition Tool" again to sync the partition table. Then reboot. Linux should be functional now.

Installing Windows

I used a Windows XP Pro SP3 install CD. I recommend that you find install media that has Service Pack 3 already installed because during my testing I used SP2 media and had a problem with it. Windows will install fine but in order to have a fully functional and more secure Windows you have to install all of the updates... and before the network card will work you'll have to install the Boot Camp drivers (located on your Mac OS X install media). After installing the Boot Camp drivers I was unable to get Service Pack 3 to install. It always gave me an error about there not being enough disk space for the SP3 update even though there were tens of GBs of free disk space. While there may be a way around using SP2 media and getting the SP3 update to install, it just seems to go more smoothly if you use install media that already has SP3 installed. Supposedly Vista works fine (and probably Windows 7) but I haven't tried them.

Boot the Windows install media just like you did the Linux install media. Install Windows just like you normally would as I'm not going to cover the normal installation steps. The only difference is that you need to make sure you select the remaining MS-DOS partition as the target and format it as NTFS. I've always selected the NTFS Quick format option. If you want, I guess you could format it as FAT32 but I don't recommend that unless you have a good reason to do so.

Anyone who has installed Windows knows that it is a two stage/boot process. The first stage lets you pick the partition, format it, and then copies all of the data files it needs to the hard drive. Then you have to reboot to the second stage where it actually has a GUI interface and installs everything... and of course, asks you for the license key. When the machine reboots you'll get the rEFIt menu as usual. I find that it is a good idea to "Start the Partition Tool" and reboot even though it tells you nothing has changed. It seems to go better that way although maybe I'm just imagining it. I have had a few occasions where the second pass refused to boot on the first attempt and it ended up just sitting at a black screen. I just cycled the power and tried again and it worked.

After the second stage is done and it reboots, again from the rEFIt menu select "Start the Partition Tool" and reboot. Again, it may or may not be required but it seems to avoid little quirks.

After installing Windows the first thing you want to do is install the Boot Camp drivers so all of your hardware works properly... especially the NIC... so the next thing you can do is install the remaining Windows updates.

Conclusion

With both Linux and Windows installed and rEFIt bootloader letting you easily pick between Mac OS X, Linux and Windows, at boot time... the job is all done.

The instructions I give above I've used at least a half dozen times on a half dozen machines and it has always worked for me. As Mac hardware changes and updates to Mac OS X happen... and depending on what Linux distros or Windows versions you use... the recipe might need slight modifications for your tastes. Please feel free to provide feedback in the comments so we can keep this information as up-to-date as possible.

I would like to offer up a big "thank you" Ashley AT csse.uwa.edu.au for the original HOWTO that educated me enough on the process to do my first successful triple-boot install.